In the construction industry, it is often necessary to grade a surface for various reasons, such as paving, installing walkways, landscaping etc. It is also necessary to dig holes for foundations, basements, swimming pools and the like. Excavation which includes digging and grading is accomplished via an operating implement, such as a grading bucket, digging bucket, grapple, hammer, screening bucket etc., which is disposed at the outer end of a telescoping boom or a jointed boom.
Excavation using a jointed boom is accomplished via a backhoe. The jointed boom works well for digging because the jointed boom operates at a quick speed. However, the jointed boom is rather difficult to control for grading purposes. Thus, a separate bulldozer must be brought on site for grading.
An excavation apparatus 100 having a telescoping boom is known in the industry as a Gradall® which is depicted in FIG. 1 as a prior art reference. Gradall's® are manufactured and sold by Gradall®, New Philadelphia, Ohio.
A Gradall® typically contains a vehicle base 118 or frame which rolls on wheels or, for more difficult terrain, tracks 112. An operator sits in a cab 120 which is mounted to the vehicle base 118. The cab 120 typically rotates or swings horizontally on the vehicle base 118. A boom support member 132 is disposed off to one side of the cab 120.
The cab 120 rotates on a fulcrum disposed on the vehicle base, which allows the operator to rotate the telescoping boom to define the excavation stroke.
The telescoping boom includes a rotating fixed boom which is fixedly secured to a rotating plate within the boom support member. A worm gear, known in the art, turns the rotating plate thus rotating the fixed boom about its longitudinal axis, thus allowing the operator to define the grading angle.
The boom support member is fixedly secured to a pivot plate which pivots rotationally about the side of the cab. A pivot plate hydraulic cylinder controls such pivoting, thus adjusting the angle of the telescoping boom relative the plane of the earth, which either defines the angle of excavation or allows the telescoping boom to be removed from the excavation surface for rotation or movement.
An outer boom 146 extends and retracts within the fixed boom 144. The grading bucket is disposed at the end of the outer boom 146. An axially aligned hydraulic cylinder 111 controls the extension and retraction of the outer boom 146. Thus, the operator sets the cab 120 for the direction of the grading stroke, sets the pivot plate for the proper grading angle, extends the outer boom 146 the appropriate length, adjusts the worm gear to define the grading angle and then works the grading bucket and then retracts the outer boom 146 to finish the grade or dig.
The main problem with this telescoping boom is that it works too slow to be efficient for various tasks. The axially aligned hydraulic cylinder 111 that controls the extension and retraction of the outer boom contains a very long piston that must be moved the same length as the movement of the outer boom. Thus, the operation of the outer boom is slow.
Further, and more importantly, a large amount of hydraulic fluid must be moved to force the movement of the within cylinder. Moving such large amount of hydraulic fluid repeatedly during strokes builds up heat. The built up heat wears out the hydraulic cylinder and causes the hydraulic fluid lines to develop cracks.